The present invention relates to an apparatus that monitors the tire condition such as tire pressure. More specifically, the present invention pertains to a casing of a transmitter that is installed inside a tire for transmitting information concerning tire condition to a receiver in the vehicle.
Pursuant to 35 USC xc2xa7 119, this application claims the benefit of Japan Patent Application No. 2001-362157 filed Nov. 28, 2001.
As shown in FIG. 10(a), a conventional transmitter 101 disclosed in Japanese Laid-Open Patent Publication No. 2000-81358 transmits tire pressure information to a receiver (not shown) in a vehicle. The transmitter 101 includes a rectangular box-shaped casing 102 and a valve stem 103, which is formed integrally on the casing 102. An air hole 104 is formed on the top surface of the casing 102. The casing 102 accommodates a pressure detector, a signal processing circuit, an electronic substrate, and a battery (not shown).
As shown in FIG. 11, the transmitter 101 is attached to a predetermined part of a wheel 112 such that the casing 102 is located inside a tire 9. Air is injected into the tire 9 from the valve stem 103 through the air hole 104.
If the electronic substrate, which is accommodated in the casing 102, is excessively close to the wheel 112, the electric wave characteristics deteriorate. Therefore, the electronic substrate is accommodated in the casing 102 to be furthest from the wheel 112.
As shown in FIGS. 10(a) and 10(b), a flange 105 extends outward from the bottom of the casing 102. Angular reinforcement ribs 106 are located between the flange 105 and the circumferential surface of the casing 102. Each reinforcement rib 106 has an inclination angle xcex8.
FIG. 7 is a perspective view of a typical tire detaching apparatus 111. The tire detaching apparatus 111 includes a turntable 115 having fixed hooks 114 and a roller 113, which is located above the turntable 115. To remove the tire 9 from the wheel 112, the roller 113 is inserted between a lower bead 9b of the tire 9 and the wheel 112, and is engaged with the lower bead 9b. Then, the lower bead 9b is lifted by the roller 113 while rotating the wheel 112.
FIGS. 8(a) to 8(d) show processes for removing the tire 9 from the wheel 112. FIG. 9 shows the relationship between the lower bead 9b and the transmitter 101 when removing the tire 9 from the wheel 112. On the assumption that a line S0, which is perpendicular to the axis of the wheel 112 and lies along the air hole 104, is zero degrees, the lower bead 9b starts to slide over the transmitter 101 at a portion that is approximately 45 to 60 degrees from the line S0 about the air hole 104 of the transmitter 101. The inclination angles xcex8 of two reinforcement ribs 106 at the portion of the transmitter 101 where the lower bead 9b slides over are set within the range of 45 to 60 degrees.
When the inclination angle xcex8 of each reinforcement rib 106 is within 45 to 60 degrees, the lower bead 9b smoothly slides over the transmitter 101. However, the inclination angle xcex8 of each reinforcement rib 106 is relatively small. Thus, when the lower bead 9b contacts each reinforcement rib 106, a relatively large bending moment is applied to the casing 102 in a direction to force the casing 102 downward as viewed in FIG. 10(b).
However, depending on the shape of the wheel 112, a relatively large space is formed between the bottom of the transmitter 101 and the wheel 112. If the space is formed, the casing 102 may deform or be damaged by the bending moment that forces the casing 102 downward. Further, since the reinforcement ribs 106 and the flange 105 project from the casing 102, the lower bead 9b might slip in the space and be caught by the casing 102. Therefore, the transmitter 101 needs to be removed from the wheel 112 beforehand. To remove the transmitter 101, an operator needs to loosen a screw, which is not shown, and drop the transmitter 101 in the inner space of the tire 9. Thus, the operation for removing the tire 9 is troublesome.
The objective of the present invention is to provide a transmitter casing for a tire condition monitoring apparatus that sufficiently endures pressure applied by a tire when removing the tire from a wheel, and permits a tire to be easily removed from the wheel.
To achieve the above objective, the present invention provides a casing for a transmitter. The transmitter is attached to a wheel such that the transmitter is located inside a tire. The transmitter transmits information concerning the tire condition. The casing includes an upper plate, a lower plate, a surrounding wall, and a pair of skirts. The lower plate faces the upper plate. The surrounding wall extends between the upper plate and the lower plate, and includes a front surface and a pair of side surfaces, which intersect the front surface. Each skirt is located at one of corners defined between the front surface and the side surfaces. Each skirt is curved such that the front surface and the corresponding side surface are smoothly connected. The skirts are inclined with respect to the lower plate at an angle in the range of 65 to 75 degrees.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.